The field of the disclosure relates generally to medical devices, and more specifically, to methods of manufacturing medical devices.
Many micro instruments that are intended to grasp or cut tissue share a common method of actuation. Generally, an elongate tube forms the outer portion of the operationally functional portion of the instrument. A rod or wire generally is enclosed by the elongate tube. Both members share a common axis. A handle, which takes many forms depending on the application, is attached to both the rod and tube. Actuation of the actuating mechanism in the handle causes relative motion of the rod and tube. In many instances, the relative motion is lengthwise along the common axis but in some instances the motion is radial around the common axis. In many instruments that are designed for grasping tissue, a distal portion of the rod is split axially forming two arms. The arms are formed so that they are biased away from each other and the central axis of the instrument when they are in a relaxed state. A grasping surface is formed on the end of each arm. In operation, the axial motion of the tube relative to the rod causes the tube to either allow the arms to relax and open the grasping surfaces away from each other or restrain the arms and cause the grasping surfaces to come together.
Manufacturing of the rod, arms, and grasping surface has conventionally been accomplished using several methods with limited success in meeting both precision and cost goals. One method includes machining, from a blank, the rod with a block on one end as a single piece. Subsequent operations using a wire electric discharge machine cuts the shape of the grasping surface and a split along the rod to form the arms. The rod is rotated and additional operations of the electric discharge machine are performed to form the complex shape of the grasping surface. Such manufacturing methods have limitations, especially as the desired size of the rod and grasping surfaces are decreased. Variation in the straightness of the rod, especially if heat treated, can cause undesirable geometric defects in the completed part. Also, the part is fabricated in the nearly closed position. This requires an additional operation to bend the arms in their biased outward relaxed position leaving an additional opportunity for geometric defect. If the arms aren't bent symmetrically enough, then the grasping surfaces on either arm don't align well when the arms are brought together.
Additionally, misalignment of the instrument blank within the machining device may result in the axis of the instrument arms not being on the same axis as the rod. Misalignment of a side profile of the instrument results in the instrument head, which include the arms, being offset from the axis of the actuation tube. Misalignment of a top profile of the instrument results in the arms not being symmetrical. An offset head can cause some features of the instrument to not be fully formed, and asymmetrical arms cause an imbalance in the actuation force and path of travel when the instrument is actuated. Such imbalance can cause undesired motions of the tip rather than a simple closure of the grasping surfaces on actuation. When a plurality of blanks are machined simultaneously, the results of misalignment of the instrument blank in the machine worsen because each blank's misalignment will be slightly different from each other blank, thus making repair very difficult.